Abstract

Water vapor is lighter than air; this can enhance waterevaporation by triggering vapor convection but there is little evidence. We directly visualize evaporation of nanoliter (2 to 700 nL) waterdroplets resting on silicon wafer in calm air using a high-resolution dual X-ray imaging method. Temporal evolutions of contact radius and contact angle reveal that evaporation rate linearly changes with surface area, indicating convective (instead of diffusive) evaporation in nanoliter waterdroplets. This suggests that convection of water vapor would enhance waterevaporation at nanoliter scales, for instance, on microdroplets or inside nanochannels.

Abstract

Water vapor is lighter than air; this can enhance waterevaporation by triggering vapor convection but there is little evidence. We directly visualize evaporation of nanoliter (2 to 700 nL) waterdroplets resting on silicon wafer in calm air using a high-resolution dual X-ray imaging method. Temporal evolutions of contact radius and contact angle reveal that evaporation rate linearly changes with surface area, indicating convective (instead of diffusive) evaporation in nanoliter waterdroplets. This suggests that convection of water vapor would enhance waterevaporation at nanoliter scales, for instance, on microdroplets or inside nanochannels.